This invention relates to a process for the production of perchloromethyl mercaptan, by means of a catalyst comprising lead acetate, solvent impregnated, on magnesium silicate.
Perchloromethyl mercaptan, Cl.sub.3 CSCl, also known as trichloromethanesulfenyl chloride has commercial importance as an intermediate in the manufacture of fungicides, bactericides, germicides, herbicides, soil fumigants and pharmaceuticals.
The production of perchloromethyl mercaptan was first described by Rathke, Ann. Vol. 167, at page 195 (1873). The catalyst used for this method was essentially iodine added in the quantity of 0.1 to 1% by weight. Below about 40.degree. C., the reaction occurs in accordance with the following equations: EQU (1) CS.sub.2 + 3Cl.sub.2 .fwdarw. CCl.sub.3 SCl + SCl.sub.2 EQU (2) 2CS.sub.2 + 5Cl.sub.2 .fwdarw. 2CCl.sub.3 SCl + S.sub.2 Cl.sub.2 EQU (3) CS.sub.2 + 3Cl.sub.2 .fwdarw. CCl.sub.4 + S.sub.2 Cl.sub.2
One of the disadvantages of the Rathke method is that in the chlorination substantial amounts of undesired byproducts, such as sulfur chlorides, thiophosgene, tetrachloromethane and the like are formed. This in turn causes a material lowering of the yield and also of the quality of the perchloromethyl mercaptan produced. The readily volatile byproducts such as carbon tetrachloride and sulfur dichloride can be separated from the reaction mixture by distillation, however, it is extremely difficult to separate the perchloromethyl mercaptan and sulfur monochloride. This is due to the fact that the respective boiling points of perchloromethyl mercaptan and sulfur monochloride differ only slightly from each other.
An additional disadvantage of the iodine catalyst is that it is soluble in the carbon disulfide reactant, and therefore must be continuously replenished.
The prior art has proposed several methods for improving the basic Rathke method. For example, U.S. Pat. No. 3,544,625 to Masat, discloses a method for producing perchloromethyl mercaptan by chlorinating carbon disulfide in the presence of a solution of inorganic acids, such as hydrochloric acid. U.S. Pat. No. 3,673,246 to Meyer et al, discloses a process for producing perchloromethyl mercaptan wherein carbon disulfide is reacted with chlorine on activated carbon at temperatures of about -5.degree. C. to +100.degree. C. U.S. Pat. No. 3,808,270 to Rupp et al., discloses a process for producing perchloromethyl mercaptan by reacting carbon disulfide and chlorine in a reaction zone filled with granular active carbon completely immersed in the liquid reaction mixture while maintaining temperatures in the range of about 40.degree. to about 135.degree. C. U.S. Pat. No. 3,878,243 to Zupancic discloses a homogeneous catalyst system comprising a lead salt of a carboxylic acid which is soluble in carbon disulfide.
The present invention has developed an improved catalyst system for the production of perchloromethyl mercaptan. Since this new catalyst system is a heterogeneous one, it is not consumed and can be used in a continuous process. Moreover, the undesirable side reaction of equation (3), which produces sulfur monochloride and carbon tetrachloride is diminished.